Probing semiconductor devices in wafer form is becoming more technically challenging as the pad size decreases (smaller pad pitch) and the number of pads on the device increase. FIG. 1 includes an illustration of a prior art probing system 10 that includes a test head 12 and a prober 14. The test head 12 includes contacts along a portion of its bottom surface. The probing system probes a semiconductor device substrate 17 that includes a plurality of die (semiconductor device). The substrate 17 typically is a monocrystalline semiconductor wafer. The prober 14 includes a head plate 142, a load board 144, a pogo stack 146, and a probe card 148 having probe needles 149. The combination of the load board 144, pogo stack 146, and probe card 148 forms the interface 18. One problem with the probing system 10 is aligning the interface 18 to the test head 12. This alignment can be quite problematic and time consuming.
When using the prior art probing system 10, the planarity between the interface 18 and the probe chuck 16 is typically done by replacing the probe card 148 with a fixture typically having several orifices. When adjusting for the planarity between the surface of the probe chuck 16 and the fixture, typically a manual measurement is made (i.e., a micrometer). Based on readings, the interface 18 typically is adjusted using shims. Although this is one method of making sure the probe chuck 16 is planar with the interface 18, manual measurements typically are time consuming, difficult, and require numerous iterations. This planarization sequence requires the test head 12 to be detached from the prober 14 to make the measurements.
Newer systems for probing include a direct docking system as illustrated by the probing system 20 in FIG. 2. The probing system 20 includes a test head 22 and a prober 24. An interface 28 is mounted directly to the test head 22 rather than the prober 24. The interface 28 in this particular prober 20 includes the load board 144, a modified pogo stack 222, and a probe card 148. Because the interface 28, including the probe card 148, is mounted directly to the test head 222, the fixture used for planarization for the probing system 10 in FIG. 1 cannot be used with the probing system 20 in FIG. 2.
As an alternative, optical methods have been used for examining the ends of the probe needles 149. Typically, an optical sensor can be mounted along the side of probe chuck 16 that examines the planarity of the probe needles 149 Adjustments are made using the external mounts 26 in FIG. 2. However, this method also has problems because it assumes that the plane formed by the probing needles 149 and the interface 28 are coplanar, which may not be true. Further, individual probing needles 149 can be distorted to such a degree that planarity cannot be achieved. Therefore, the probing system 20 can still have problematic planarizations.
Regardless of system and method, substrates are virtually never present during a planarization sequence. The likelihood of damage to the substrate is too high.